I have a Surefire 618FA on my Rem870, and wouldn't even consider using a shotgun for HD without one. It is absolutely essential to have some form of light when you're planning for how to defend / secure your home. Having one directly attached to your weapon, one which can absorb the violent recoil, is infinitely better than trying to hold one in your hand. Think about it, if your off hand is busy holding a flashlight, how many hands does that leave available to operate the shotgun? Also, by having it attached to your weapon, you can use your support hand to do some simple functions, such as opening a door or reaching for a telephone. Also, if you're in a hostile environment, your weapon should always be pointing in the same direction as your eyes, it's much easier to remember that if your means of seeing what you're looking at is attached to your weapon.
Additionally, I currently have a Mesa Tactical low-rise adapter on my 870, which is equipped with Scattergun Tech tritium sights. It is very comfortable. I thought the recoil might be a little harsh, but it isn't. It is not noticeably any worse than with my Speedfeed III. Although, once I get my next 870, it will be getting the Mesa adapter / AR stock, and the Speedfeed will be going back on my HD gun. I'm planning to do so because my next 870 will be getting registered as a SBS, and I want the ability to make it as short as possible without going to a PG-only or folding stock configuration.
A PG only shotgun is cool for a few rounds at the range from time to time, or as a CQB breaching weapon. (I am awaiting approval of my AOW transfer as I type. It's solely intended as a "because I can" fun toy.) However, they are awkward for much else, especially for serious "social" work. They are difficult to aim properly and recoil tends to be very aggressive. I would whole-heartedly recommend against using one for HD. If you absolutely must have as short a weapon as possible, without getting into the NFA arena, buy a folding stock. Just remember, the stock folds for storage and is meant to be unfolded for use. (Personally, I'm not much of a fan of folding stocks. I don't feel as they do enough to tame the recoil.)
Hope that helps,
Frank